1. Field of the Invention
This invention relates to disc apparatuses, and more particularly to a disc apparatus adapted to correct a track jump error due to individual disc variation.
2. Description of the Prior Art
In a conventional disc apparatus of this kind, when performing a track jump (seek) to a target position, tracks to be jumped over is first determined in number by calculation and a jump is then effected according to the determined number of tracks. As a result of the jump, when a pickup goes beyond the target position (overshoot) or does not reach the target position (undershoot), the disc is judged as one that is liable to overshoot or undershoot. When a track jump is later performed with the same disc, a correcting value for the overshoot or undershoot, i.e. a value (.alpha.) taking a disc-manufacturing variation into consideration, is added to or subtracted from the calculated number of tracks, thereby obtaining an accurate seek to a target position.
In the prior art, however, the result of the track jump first made is utilized to compensate for the number of tracks to be jumped later. Accordingly, it has been difficult for a pickup to accurately access to a target position in a track jump immediately after a disc is mounted for the first time on the apparatus. That is, it is a conventional practice to add or subtract a predetermined value (.alpha.) to or from the number of tracks to be jumped over, without examining factors encountered in overshoot or undershoot.